The invention relates to flame-resistant HR cold-cure moulded foams with reduced smoke intensity and toxicity, a process for the preparation thereof and the use thereof.
Cold-curing polyurethane flexible moulded foams are used, inter alia, as seats, back and arm rests or head rests in automobiles, track vehicles and water-craft, aeroplanes and in the furniture sector. In all the above-mentioned sectors, the flame resistance of the foams is an important factor. The requirements in respect of flame resistance are very stringent in the case of track vehicles, aeroplanes and furniture in particular. In order to meet the relevant standards, such as, e.g., BS 5852, Part 2, Crib Ignition Source V, CSE RF4/83 or UIC 564/2 or and DIN 54341, ASTM E 162; California TB 133, melamine is added to the foam as a flame retardant. A disadvantage of this is that a solid has to be stirred into the polyol formulation with the development of dust. Moreover, the melamine solid settles out of the polyol formulation, making processing difficult. The sedimentation of melamine may be prevented by the use of specially stabilised melamine dispersions in polyethers, as described in DE-OS 195 40 809 and EP-A 835 905. Moreover, the mechanical properties of the foams, particularly the tensile strength, elongation at break and tear propagation resistance are adversely affected by the incorporation of melamine in the polymer matrix of the foam. A further disadvantage is that high smoke intensities and toxicities occur during combustion.
It follows from xe2x80x9cPolyurethanes World Congress 1991xe2x80x9d, Technomic Publishing, Basel, Lancaster 1991, p. 615 ff that flame-resistant HR slabstock foams can be obtained by the combination of pure toluene diisocyanate with a PHD polyol and liquid phosphorus halogen compounds. An HR cold-cure moulded foam produced with these components does not, however, meet the requirements laid down in BS 5852 Part 2, Crib V, this possibly being attributable to the different polymer structure in slabstock foam and moulded foam. The results obtained on slabstock foam cannot, therefore, be transferred to moulded foam.
It has now been found that by reacting mixtures of TDI and MDI with PHD or PIPA polymer polyols, it is possible to obtain HR cold-cure moulded foams with reduced flammability, smoke density and toxicity.
The invention provides, therefore, an HR cold-cure moulded foam which may be obtained by reacting
a) mixtures of TDI and MDI in the weight ratio 95:5 to 60:40 with
b) dispersions of polymers containing relatively high molecular weight hydroxyl compounds which were prepared by reacting mono- and/or polyisocyanates with polyamines and/or hydrazines and/or hydrazides and/or alkanolamines having primary and/or secondary amino groups in a polyether having 1 to 8 primary and/or secondary hydroxyl groups with a number-average molecular weight from 400 to 16000,
c) in the presence of chemical and/or physical blowing agents (specially water), and
d) optionally flame retardants which are liquid and/or soluble in a), b) or c), and/or
e) optionally compounds with at least two hydrogen atoms which are reactive towards isocyanates and with a molecular weight from 32 to 399, and/or
f) optionally further auxiliaries.
According to the invention, mixtures of toluene diisocyanate (TDI) and diphenylmethane diisocyanate (MD) are used as component a). The weight ratio between TDI and MDI is 95:5 to 60:40, preferably 95:5 to 70:30, particularly preferably 95:5 to 80:20. The isomer ratio of 2,4-TDI to 2,6-TDI may be from 100:0 to 65:35. In the MDI used, the content of binuclear diisocyanates, i.e. 2,2xe2x80x2-MDI, 2,4xe2x80x2-MDI and 4,4xe2x80x2-MDI is preferably between 35 and 100 wt. %, wherein 2,4xe2x80x2-MDI accounts for a proportion from 0 to 60 wt. % of the total amount of MDI. Higher homologues of the mixtures containing the MDI series (xe2x80x9cpolymeric MDIxe2x80x9d, xe2x80x9ccrude MDIxe2x80x9d) may also be used. According to the invention, both TDI and MDI may be modified in a manner known to the expert, as described in G. Oertel (ed.): xe2x80x9cKunststoff-Handbuchxe2x80x9d, Vol, VII, Carl Hanser Verlag, 3rd edition, Munich 1993, p. 91-97, i.e., for example, to form an allophanate, biuret, trimer, carbodiimide, or prepolymerised with polyethers or parts of component b). If mixtures are used in which an isocyanate component is modified with polyethers or parts of component b), then the weight ratio of TDI to MDI is calculated on the basis of the unmodified isocyanates.
According to the invention, the polyol component b) contains dispersions of polymers containing relatively high molecular weight hydroxyl compounds which were prepared by reacting mono- and/or polyisocyanates with polyamines and/or hydrazines and/or hydrazides and/or alkanolamines having primary and/or secondary amino groups in a polyether having 1 to 8 primary and/or secondary hydroxyl groups with a number-average molecular weight from 400 to 16000 (xe2x80x9cbase polyolxe2x80x9d). Base polyols with a number-average molecular weight from 1500 to 8000 are used in preference. Hydroxyl compounds used in preference are those which were prepared by reacting polyether polyols with hydrazines (PHD polyols). The component b) preferably has an average OH functionality from 2.0 to 3.5. Polyether polyols used in preference are those which have a primary OH group content of at least 60 mole %, preferably at least 70 mole %. In a further preferred embodiment, the component preferably contains, in addition to a base polyol with an ethylene oxide content of at most 40 wt. %, at least one other polyether polyol with an average functionality from 2 to 6, a number-average molecular weight from 1500 to 12000 in an amount from 1 to 50 wt. %, based on the total amount of compound b) with an EO content of more than 40 wt. %. This embodiment leads to better skin formation, a greater open-cell character and allows more scope for adjusting the NCO/OH index and hence better processability of the formulation. The foam obtained has increased elasticity and its hardness, which may be high due to the polymer dispersion, is reduced to such an extent that even flexible moulded parts may be produced.
Chemical and/or physical blowing agents c) are used for the preparation of the foams according to the invention. The chemical blowing agent used as component c) is preferably water which yields carbon dioxide as blowing gas by reaction with isocyanate groups. Water is used preferably in an amount from 2 to 8 wt. %, particularly preferably 2 to 4 wt. %, based on the amount of component b). Carbon dioxide may, however, also be added to the polyol or isocyanate component as a gas or in the liquid form, online or in the batch process according to inherently known methods. In component c) it is also possible to use non-flammable physical blowing agents such as, e.g., dichloromethane, dichloromonofluoromethane, difluoromethane, trifluoromethane, difluoroethane, 1,1,1,2-tetrafluoroethane, tetrafluoroethane (R 134 or R 134a), 1,1,1,3,3,3-hexafluoropropane (R 356), 1,1,1,3,3-pentafluoropropane (R 245fa), chlorodifluoroethane, 1,1-dichloro-2,2,2-trifluoroethane, 2,2-dichloro-2-fluoroethane, heptafluoropropane and sulfur hexafluoride. Mixtures of said blowing agents may also be used. As the blowing agent escapes almost completely from the foam during the production process, low-boiling hydrocarbons, e.g., pentane, hexane and isomers thereof may also be used. Other suitable blowing agents are carboxylic acids such as formic acid, acetic acid, oxalic acid and chemical blowing agents which liberate gases during the foaming process, such as, e.g., carbamates. These blowing agents are used preferably in combination with water.
Optionally, liquid flame retardants d) which are liquid and/or soluble in one or more of components a), b) or c) are used for the preparation of the foams according to the invention. Commercial flame retardants containing phosphorus are used in preference, for example, tricresyl phosphate, tris-(2-chloroethyl) phosphate, tris-(2-chloropropyl) phosphate, tris-(2,3-dibromopropyl) phosphate, tris-(1,3-dichloropropyl) phosphate, tetrakis-(2-chloroethyl) ethylene diphosphate, dimethylmethane phosphonate, diethylethane phosphonate, diethanolaminomethylphosphonic acid diethyl ester. Halogen- and/or phosphorus-containing polyols with a flame retardant effect are also suitable. The flame retardants are used preferably in an amount of at most 35 wt. %, preferably at most 20 wt. %, based on component b).
Compounds with at least two hydrogen atoms which are reactive towards isocyanates and with a molecular weight from 32 to 399 e) are also optionally used in the preparation of the foams according to the invention. These are taken to mean compounds having hydroxyl groups and/or amino groups and/or thiol groups and/or carboxyl groups, preferably compounds having hydroxyl groups and/or amino groups, which act as chain extenders or crosslinking agents. Said compounds generally have 2 to 8, preferably 2 to 4 hydrogen atoms which are reactive towards isocyanates. Examples thereof are described in DE-OS 28 32 253, p.10-20. In a preferred embodiment, mixtures of at least two of these chain extenders and/or crosslinking agents are used. Preferred chain extenders and/or crosslinking agents are, for example, glycerol, ethylene glycol, diethanolamine, triethanolamine and triisopropanolamine.
Optionally other auxiliaries and additives f) may also be used in the preparation of the HR cold-cure moulded foams according to the invention. These are, for example, catalysts which accelerate the reaction between the isocyanate component a) and the polyol component b). Examples of suitable catalysts are organic tin compounds such as tin (II) salts of organic carboxylic acids, e.g., tin (II) acetate, tin (II) octoate, tin (II) ethyl hexanoate and tin (II) laurate and the dialkyltin (IV) salts, e.g., dibutyltin diacetate, dibutyltin dilaurate and dioctyltin diacetate. Other examples of suitable catalysts are amines such as dimethylaminopropyl urea, dimethylaninopropylamine, bis(dimethylaminopropyl)amine, diazabicyclooctane, dimethylethanolamine, triethylamine, dimethylcyclohexylamine, dimethylbenzylamine, pentamethyldiethylene triamine, N,N,Nxe2x80x2,Nxe2x80x2-tetramethylbutane diamine, N-methylmorpholine, bis(dimethylaminoethyl)ether and tris(dialkylaminoalkyl)-s-hexahydrotriazines. The catalyst component contains preferably at least one aliphatic amine. A combination of several catalysts may also be used. It is also possible to use, for example, paraffins or fatty alcohols or dimethyl polysiloxanes, and pigments or dyes, and stabilisers against ageing and weathering influences, plasticisers such as dioctyl phthalate and fungistatic and bacteriostatic substances. These are usually added to the polyol component in amounts from 0 to 10 parts by weight, preferably 0 to 5 parts by weight. Other examples of surfactant additives and foam stabilisers and cell regulators, reaction inhibitors, stabilisers, flame-retardant substances, dyes and fungistatic and bacteriostatic substances which may also optionally be used, and details about the mode of use and mode of action of said additives are described in G. Oertel (ed.), xe2x80x9cKunststoff-Handbuchxe2x80x9d, Vol. VII, Carl Hanser Verlag, 3rd edition, Munich 1993, p.110-115 and DE-OS 27 32 292.
The reaction components are usually reacted according to the inherently known one-stage process, the prepolymer process or the semi-prepolymer process, mechanical equipment often being used, e.g. that described in U.S. Pat. No. 2,764,565. Details about processing equipment which is also suitable according to the invention are described in R. Vieweg, A. Hxc3x6chtlen (ed.): xe2x80x9cKunststoff-Handbuchxe2x80x9d, Vol. VII, Carl-Hanser Verlag, Munich 1966, p. 121-205. According to the invention, foaming is carried out preferably in closed moulds. The reaction mixture is introduced into a mould. Suitable mould material includes metal, e.g. aluminium or plastic, e.g. epoxy resin. The expandable reaction mixture foams in the mould and forms the moulded article. According to the invention, a suitable procedure in this connection is to introduce expandable reaction mixture into the mould in such an amount that the foam formed just fills the mould. It is also possible, however, to operate such that more expandable reaction mixture than is required to fill up the inside of the mould with foam is introduced into the mould. In the latter case, operations are carried out with xe2x80x9cover-chargingxe2x80x9d; such a mode of operation is known, e.g., from U.S. Pat. Nos. 3,178,490 and 3,182,104.
The preparation of the foams according to the invention is carried out preferably in such a way that the NCO/OH index, i.e. the stoichiometric ratio between reactive isocyanate groups and hydroxyl groups multiplied by 100, is between 65 and 120. The NCO/OH index is particularly preferably 70 to 110.
The density of the moulded articles obtained is preferably 30 to 120 kg/m3. In a preferred embodiment of the invention, the ratio of components is selected such that the filler content of the foam formulation, i.e., the proportion of dispersed polymer components contained in component b) to the total amount of foam formulation, is 3 to 30 wt. %, preferably 4 to 16 wt. %.
The invention also provides the use of the foams according to the invention as upholstery material for, e.g., seats, back and arm rests and head rests in automobiles, track vehicles, aeroplanes and water-craft and in furniture for private and public uses.